(19)
(11) EP 0 396 886 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
05.08.1992 Bulletin 1992/32

(43) Date of publication A2:
14.11.1990 Bulletin 1990/46

(21) Application number: 90105507.9

(22) Date of filing: 23.03.1990
(51) International Patent Classification (IPC)5: H04M 9/08, H04M 1/60, H03K 17/62
(84) Designated Contracting States:
DE FR GB IT

(30) Priority: 08.05.1989 US 348459

(71) Applicant: MOTOROLA, INC.
Schaumburg, IL 60196 (US)

(72) Inventor:
  • Bader, Scott K.
    Mesa, Arizona 85210 (US)

(74) Representative: Hudson, Peter David et al
Motorola European Intellectual Property Midpoint Alencon Link
Basingstoke, Hampshire RG21 7PL
Basingstoke, Hampshire RG21 7PL (GB)


(56) References cited: : 
   
       


    (54) Current switch for use in telephony systems or the like


    (57) A current switch (40) that is responsive to logic switching control signals (C, B, D) is used in a telephone circuit comprising a handset receive signal path and a speakerphone receive signal path for separation a received voice signal into either the handset or speakerphone receive path depending on the selected mode of operation of the telephone circuit. The current switch includes a pair of switched current mirrors (40,82) and clamp circuits (160,180) which are rendered active or inactive depending on the particular mode of operation. The clamp circuits maintain the dc voltage appearing at the input of each current mirror constant as the particular current mirror is switched between active and inactive states thereby inhibiting audible dc transients.







    Search report